Chris Kuklewicz wrote:
Simon Marlow wrote:
Spencer Janssen wrote:
Earlier today on the #haskell IRC channel, Tim Toorop (bolrod on #haskell) pointed out that Data.List.inits is rather slow, and proposed an alternative. After some collabrative tweaking, we came up with the following:
inits xs = [] : (zipWith take [1..] $ map (const xs) xs)
I propose to replace inits in Data.List with this one. Objections about the relaxed strictness are noted, but I subscribe to the view that the original is more strict than necessary, and the general trend for Data.List functions is to be as lazy as possible.
Cheers, Simon
If the goal is speed, then this definition is running over 10% faster with ghc -O2 on my powerbook for (sum $ map length $ inits [1..10000])
inits' = helper id where helper f [] = (f []):[] helper f (x:xs) = (f []):helper (f.(x:)) xs
Seems to be quite faster in some cases! Though other cases it's a bit slower. Probably depends on the thing you want to use the inits for which one might be better. Though with getting the actual contents of inits (like with sum $ map sum $ intis) yours sure is faster! -- Tim Toorop